1. Field of the Invention
This invention relates to a magenta toner used in full-color copying machines and printers for developing electrostatic latent images in electrophotography, electrostatic recording, electrostatic printing and so forth, and to a process for producing the magenta toner.
2. Related Background Art
Conventionally, electrostatic printing, electrophotography and so forth are available as processes for developing electrostatic latent images by the use of toners to form visible images. In these processes, electrostatic latent images are formed on a photosensitive member, subsequently the electrostatic latent images are developed by the use of toners to form toner images, then the toner images are transferred to a transfer material such as paper as occasion calls, and thereafter the toner images are fixed by the action of heat, pressure, heat-and-pressure, solvent vapor or the like to obtain copies or prints.
In recent years, in image forming apparatus such as copying machines and printers, the evolution from monochrome colors to full colors is being in rapid progress, where full-color image forming apparatus have been put into practical use and it has become able to obtain high-quality images which are of course superior in resolution and gradation and also in color reproducibility free of color non-uniformity.
For example, in full-color copying machines, a color-image original is color-separated into B (blue), G (green) and R (red) with use of corresponding color filters, and thereafter latent images formed of dots of 20 to 70 μm in diameter which correspond to an original image are developed by the use of respective-color toners of Y (yellow), M (magenta), C (cyan) and B (black), utilizing the action of subtractive color mixing.
As conventional magenta colorants for electrophotography, proposed are quinacridone pigments, anthraquinone pigments, thioindigo pigments, xanthene dyes, xanthene pigments, azo dyes, azo pigments and so forth (Japanese Patent Publications No. S49-46951 and No. S55-42383, and Japanese Patent Applications Laid-open No. S55-26574, No. S59-57256 and No. 2000-248191). In particular, xanthene dyes are preferred in view of chroma and brightness. However, the xanthene dyes have had a problem on fastness such as light-fastness. To solve such a problem, phenylxanthene dyes substituted with a branched alkyl group are proposed, which, however, have solubility in water or are insufficiently soluble in polymerizable monomers, and hence it has been difficult for them to be used in direct suspension polymerization (Japanese Patent No. 02916835).
A method is also known in which, in order to further control colorant transparency and color tints, a coloring compound is not used alone, and a pigment and a pigment, or a pigment and a dye, are mixed, or a quinacridone pigment is used in the state of mixed crystals (see Japanese Patent Applications Laid-open No. H1-224777 and No. S62-291669).
These magenta colorants have good affinity for binder resins and good light-fastness, and can provide magenta toners having superior triboelectric charging characteristics and color tones. However, as the full-color image forming apparatus have become more highly functional in recent years, magenta toners are demanded to be more improved in color tones, chroma, transparency, electrophotographic performance and so forth.